Integrateable capacitors and microcoils, and methods of making such integrateable capacitors and microcoils are described.
Efforts are being made to integrate inductors on semiconductor substrates, e.g., silicon and gallium arsenide integrated circuits. Known structures employ spirals parallel to the underlying substrate. When such structures are made on a substrate that is slightly conductive such as silicon, the coil magnetic fields induce eddy currents in the underlying substrate. Such eddy currents cause resistive dissipation and contribute to energy loss. When such coils are operated at high frequencies, the skin and proximity effects force the current to flow along outer surfaces of the conductive material. For example, at frequencies of 900 MHz, 1.9 GHz and 2.4 GHz, the “skin depth” is about 2 to 3 μm for typical conductive materials. Because only a portion of the cross section of the conductive material is utilized, AC resistance of the coil is significantly higher than the DC resistance of the coil.
Micro-fabricated capacitors and micro-fabricated inductors based on released 3D structures and MEMS processing, i.e., processes used to manufacture micro-electromechanical structures, offer improved electrical performance over components that are manufactured using planar IC processing. MEMS processing enables near ideal geometries with high Q, i.e., high quality factor. MEMS variable capacitors offer larger RF signal levels and less high-frequency distortion. Out-of-plane coil inductors manufactured using MEMS processing minimize eddy current loss. Process integration of high performance capacitors and inductors with integrated circuits is challenging.